This invention is related in general to the field of antennas, and more particularly, to a microstrip phase shifting reflect array antenna.
Many radar, electronic warfare and communication systems require a circularly polarized antenna with high gain and low axial ratio. Conventional mechanically scanned reflector antennas can meet these specifications. However, they are bulky, difficult to install, and subject to performance degradation in winds. Planar phased arrays may also be employed in these applications. However, these antennas are costly because of the large number of expensive GaAs Monolithic microwave integrated circuit components, including an amplifier and phase shifter at each array element as well as a feed manifold and complex packaging. Furthermore, attempts to feed each microstrip element from a common input/output port becomes impractical due to the high losses incurred in the long microstrip transmission lines, especially in large arrays.
Conventional microstrip reflect array antennas use an array of microstrip antennas as collecting and radiating elements. Conventional reflect array antennas use either delay lines of fixed lengths connected to each microstrip radiator to produced a fixed beam or use an electronic phase shifter connected to each microstrip radiator to produce an electronically scanning beam. These conventional reflect array antennas are not desirable because the fixed beam reflect arrays suffer from gain ripple over the reflect array operating bandwidth, and the electronically scanned reflect array suffer from high cost and high loss phase shifters.
In U.S. Pat. No. 4,053,895 entitled xe2x80x9cElectronically Scanned Microstrip Antenna Arrayxe2x80x9d issued to Malagisi on Oct. 11, 1977, antennas having at least two pairs of diametrically opposed short circuit shunt switches placed at different angles around the periphery of a microstrip disk is described. Phase shifting of the circularly polarized reflect array elements is achieved by varying the angular position of the short-circuit plane created by diametrically opposed pairs of diode shunt switches. This antenna is of limited utility because of the complicated labor intensive manufacturing process required to connect the shunt switches and their bias network between the microstrip disk and ground.
It is also known that any desired phase variation across a circularly polarized array can be achieved by mechanically rotating the individual circularly polarized array elements. Miniature mechanical motors or rotators have been used to rotate each array element to the appropriate angular orientation. However, the use of such mechanical rotation devices and the controllers introduce mechanical reliability problems. Further, the manufacturing process of such antennas are labor intensive and costly.
It has been recognized that it is desirable to provide a high performance circularly polarized beam scanning array antenna that is low in cost and easy to manufacture.
In one aspect of the invention, an antenna array element has an electrically conductive patch, at least two electrically conductive stubs positioned along the periphery of the patch, and at least two switches each operable to connect or disconnect the patch to one of the at least two stubs.
In another aspect of the invention, an antenna includes an array of electrically conductive patches arranged in a predetermined generally equally spaced pattern on a first surface of a substantially flat substrate, at least two electrically conductive stubs positioned along the periphery of each of the patches, and at least two switches coupled between each patch and the at least two stubs. A controller is coupled to each of the at least two switches operable to connect or disconnect a selected one of the at least two stubs to each patch.
In another aspect of the present invention, a method of electronically phase shifting array elements in a reflect array antenna includes the steps of generating and directing energy toward N sets of patches disposed on a substantially flat surface and arranged, in a predetermined pattern thereon, selectively connecting patches, for each of N sets of patches, to a different stub out of N stubs arranged along half of the periphery of each patch, thereby applying a phase shift to the energy, reradiating into space.
In yet another aspect of the present invention, a method of electronically phase shifting array elements in a reflect array antenna includes the steps of generating and directing energy toward N sets of patches disposed on a substantially flat surface and arranged in a predetermined pattern thereon, selectively connecting patches, for each of N sets of patches, to a different pair of diametrically opposed stubs out of N pairs of diametrically opposed stubs arranged along the periphery of each patch, thereby phase shifting the energy, and reradiating the energy into space.